An exhaust gas after-treatment system for a modern diesel engine exhaust system typically incorporates a particulate filter for collecting and disposing of sooty particulate matter. A typical particulate filter acts as a trap for removing the particulate matter from the exhaust gas system. In many instances, the particulate filter may be regenerated or cleaned using superheated exhaust gas to burn off the collected particulate.
The pressure drop across the particulate filter may ordinarily be a good proxy for accumulated soot therein in steady-state or highway driving conditions. In other drive cycles, such as stop-and-go cycles and other transient conditions, it is more difficult to estimate an amount of soot accumulated in the particulate filter via a strict resistance flow or exhaust gas pressure drop calculation across the particulate filter due to a changing volumetric flow rate of the exhaust gas passing through the exhaust gas system.